The purpose of the proposed research is to utilize tritium labeled Gonadotropin Releasing Hormone (H3-GnRH) to study its metabolism and molecular interactions in the hypothalamic-pituitary unit and in the peripheral circulation. High specific activity H3-GnRH will be labeled by a tritium atom method using microwave discharge activation of tritium gas. This method has been shown to be particularly well suited to the preparation of tritiated peptides in which each amino acid is labeled. Biological activity of the tritium labeled molecules will be demonstrated in an in vivo bioassay and the amino acid tritium distribution in the H3-GnRH recovered in the pituitary will be compared to that in the injected material to ensure homogenous behavior of the tritiated molecules. All studies will be carried out in both rats and rhesus monkeys. The peptide fragments and/or derivatives resulting from peripheral metabolism of 3H-GnRH will be determined and the principal sites responsible for its biological inactivation will be documented. The mechanism of the rapid clearance of GnRH will be sought at a cellular level and the enzyme(s) presumed to be involved will be isolated and characterized. The possibility that molecular alterations and/or binding at the hypothalamic-pituitary level may play a role in physiology of GnRH action on the pituicyte will be studied. Utilizing the products of H3-GnRH metabolism which re-enter the blood after biological inactivation and are excreted into urine, we will measure the GnRH production by urinary isotope dilution techniques. We will also attempt to establish the chemical structure of GnRH-activity isolated in microgram quantities from hypothalami and portal blood of species in which its structure is not yet established. It is hoped that these studies will shed light both upon the physiology of GnRH and upon its pharmacologic applications. In addition, we anticipate that these studies will serve as models for more extensive studies of peptide hormone metabolism.